ABSTRACT
A cross-sectional study was undertaken to determine the water holding capacity (WHC) of beef sold in selected butcher shops of Mekelle, Ethiopia and to establish the effects of pre-slaughter rests and age of the animals with pH and WHC of the meats. A total of 80 samples from 80 randomly selected butcher shops were sampled in 6 months study period of time, from May to October. Each sample was accompanied by questionnaires. The meats were taken to the laboratory to measure pH and water holding capacity using the filter paper press and drip loss methods. The means and standard deviations of filter paper press and drip loss were found as 49.4 ± 5.85 and 4.58 ± 0.96, respectively. The age of the slaughtered animals had significant association (p<0.05) with the pH measured at 24 h post-slaughter, drip loss and filter paper press measurements. The pre-slaughter rest period had strong effect on pH (p<0.05) at 3 h post-slaughter. The present study concluded that water holding capacity and pH as quality indicators of meat are influenced by age and pre-slaughter rest of the slaughtered animals.
Key words: Age, drip loss, filter paper press, pH, pre-slaughter stress.
Muscle is a tissue that consists predominantly of contractile cells of animals. It has different spatial arrangements of myofibrils. The spatial arrangement of the fibrilar network of muscle has great role in the quality of the meats (Bowker et al., 2014). The pH of muscle is approximated from 6.9 to 7.0. The variation in pH may come from physical exercise, nutritional deficiencies, age, sex and/or other factors of the animals (Zhang et al., 2010; Simela, 2005; Simela, 2004). Muscle is converted into meat during the processes of rigor mortis. In the pre rigor stage, the muscle is converted into the stage of rigor and it becomes changed into meat. Fresh meat contains approximately 70 to 75% water, 15 to 20% protein, 5 to 10% lipids or fat and oils, 1 to 2% carbohydrates and 1% vitamins and minerals. At the rigor stage of meat, the amounts of these contents may be changed (Simela, 2005). Meat is said to be quality if it is suitable for use in specific products. The water holding capacity, the rate of decline in pH, flavor, juiciness, color, ethical quality and health quality are the quality indicators of meat. Good quality meat has a potential to have good water holding capacity, slow rate of declining pH, good appearance and fatty smell and does not have zoonotic diseases (Aaslyng, 2002). The quality of meat can be altered either by pre-slaughter conditions of the animals or by post mortem conditions of the meat (Miller, 2007).
Water holding capacity (WHC) of meat is defined as the ability of meat to retain the water when external force is exerted. Such forces can be exhaustive starvation and thirst, prolonged traveling on foot, extreme heat or windy air condition of the environment when the animals stay, dry or humid storage of meat, and the orientation of cutting, grinding, or processing of meat (Miller, 2007). The majority of water in meat is held within the structures of the muscle itself. It can be found within the myofibrils, between the myofibrils and the cell membrane (sarcolemma), between muscle cells and between muscles bundles (groups of muscle cells). Once muscle is harvested, the amount of water in meat can be changed depending on numerous factors related to the tissue itself and how the product is handled (Simela, 2005). Water held in the meat can have different names according to their location. Bound water is the water that is found within the protein of the meat. Entrapped water found within muscle structures. This water molecule may be held either by steric (space) effects and/or by attraction to the bound water but is not bound per se to protein. In early postmortem tissue, this water does not flow freely from the tissue, yet it can be removed by drying, and can be easily converted to ice during freezing. Entrapped or immobilized water is most affected by the rigor process and the conversion of muscle to meat. Upon alteration of muscle cell structure and lowering of the pH, this water can also eventually escape as wash out. This entrapped water is becoming free water when it is moved from the structure in pre rigor meat as a result of rigor mortis or post mortem effects. Free water is water whose flow from the tissue is unimpeded. Weak surface forces mainly hold this fraction of water in meat (Brondum et al., 2000). Maintaining as much of this water as possible in meat is the goal of meat handlers (Huff-Lonergan, 2005).
The pH level and the level of WHC of meat can be affected by the anti mortem events, such as lack of sufficient rest or extreme hot or extreme humid air condition of the lairage (pen), starvation and deprivation of water prior to slaughter of the animals for more than 12 h or the manner of handling like cutting of the meat during deboning and meat selling period of time, and while treating the meat to avoid meat spoilage can also affect the pH level and WHC of the meat (Lomiwes, 2008). This alteration of the pH level and WHC of the meat may come from the alteration of glycogen level of muscle of animals stressed during pre-slaughtered condition (Aaslyng, 2002; Miller, 2007). The stability of given meat can be ensured when the requirement of its water holding capacity is maintained and when there is a slow declining of its pH level. This means that the water holding capacity and the slowly declining of pH level of that meat have zoonotic, economic and nutritional importance (Simela, 2005). Meat inspectors and local abattoir administrators of Mekelle city mentioned that the butchers brought their animals to slaughter house directly from the local markets without getting pre-slaughter rest (Mekelle, 2016). Those animals might have travelled from a longer distance in starved condition and stressed by moving here and there in the market and sent directly to the slaughter house without giving sufficient rest prior to slaughter. Besides, most of those animals are poor in body condition, progressively exhausted in work and older age. The above-mentioned professionals and other meat consumers also mentioned that the meat found in the butcher houses in Mekelle city looks dry, dark in color and not attractive to consume it. However, the problem is not yet studied. Hence, the present work will deal with the following specific objectives.
(1) To determine the water holding capacity of beef sold in selected butcher shops of Mekelle
(2) To establish the associations between age and pre-slaughter rest with pH and water holding capacity.
Study area
The study was conducted in Mekelle city, Tigray region, Northern Ethiopia. Mekelle is an urban centre and the capital of Tigray region. The city covers an area of about 53 km2, with an estimated population of 215,546 people. It is located 783 km North of Addis Ababa (Figure 1). Currently so many regional, national and international people are visiting the city. From small to larger scales of restaurants are emerging in this city. It has 160 legal butcher houses that are distributed throughout the city and there are also some illegal butchers whose number is not determined yet (TRHDA, 2008).
Study design
A cross-sectional study was employed for the present study.
Sample size
The sample was collected from Mekelle Municipality abattoir where the legal butcher shops send their animals for slaughter. For maximum precision, samples from 50% of the butcher shops, that is 80 samples were collected.
Sampling design and sample collection
Simple random sampling technique was employed to select 80 butcher shops from the total of 160 (Mekelle, 2014) butcher houses. The longissimus dorsi (LD) muscle was taken because of its economic importance (cheapest in value in relative to the other parts of the muscle parts), long muscle and easy to sample (Preziuso and Russo, 2004). In order to know the age of the meat, all samples were taken from Mekelle Municipality abattoir. Collection of fresh meat sample was done immediately following each slaughter by labeling each sample orderly in accordance to the code of the questionnaire. To prevent moisture loss during sample collection and preparation a tightly sealed plastic tube was used.
Questionnaire survey
Each sample was accompanied by questionnaire for characteristics of the owners’ address, sex; characteristics of the slaughtered animal, the service provided, and observational characteristics of the meats.
Laboratory works
The work was conducted in the microbiology lab, college of Veterinary Medicine, Kalamino campus. The pH of the collected meat was measured using digital pH meter by probing it in to the meat for 30 to 60 s (Abraham and Kumar, 2000) and reading was recorded each sample along with its own code. Before taking the measurement it was calibrated using standard buffer solution (neutral) and it was rinsed with distilled water after taking each measurement. Firstly it was measured at 3 h period of time, and secondly, the same test was carried out at 24 h (Santos-Silva, 2001). The water holding capacity of meat was determined by two fundamentally different principles: Filter paper press method and the water drip loss method.
Filter paper press method
The external force used to drive out the water was the filter paper press method. Chromatography paper Whatman No. 40 was kept for 24 h in a dissociated 38% sulfuric acid in advance that it complies with 60% humidity and it helped to diffuse out the water freely through the paper (Kashif et al., 2014). Five grams of 24 h aged meat was homogenized on a metal plate. Out of this, 300 mg meat which was measured right after preparation was put on the Whatman paper No. 40 and then was placed between two slides on which a 100 g weight was placed on the top slide for 5 min so as to exert downward force and to release water from the meat as per the method described by Abraham and Kumar (2000).
The water released from the meat was wetting the paper and the boundary of that wetted area was demarcated using sharp pencil and was measured and reported in percentage of the ratio of the diameter of the meat to the diameter of the water wetted paper as per Mendiratta et al. (2008).
Water drip loss (Honikel bag method)
A 2.5 cm thickness slice, 2 × 5 cm width and length 24 h aged raw meat was cut parallel to the muscle fiber and hanged for 2 days in plastic sealed tube at 4°C as described by Brondum et al., (2000). The water drip out of the meat was measured and was reported in percentage of the ratio of weight of water loss to weight of meat prior to drip out the water (Diaz et al., 2010; Brondum et al., 2000; Honikel, 1998).
Data analysis
The qualitative and quantitative data were analyzed using simple descriptive and computer based statistical software (STATA 11) was used to analyze the data in order to compare means of age and pre-slaughter stress of the slaughtered animals on pH and water holding capacity of the meat. For the purpose of this study, p<0.05 was considered to be significant.
Questionnaire survey
The characteristics of the slaughtered animals had shown that the majority (65%) of the slaughtered animals were old. Only 35% of the slaughtered animals were at the stage of bull. More than half (66%) of the respondents did not have lairage for giving rest for the purchased animals before they were slaughtered. 96.3% of the slaughtered animals were Zebu breed, only 3.7% of them were crossbreed. More than 78% of the carcasses were dark in color and stored in the butcher shops for more than 24h period of time before completely sold. Only 21.3% of them were light in color and sold before 24 h of storage time.
Water holding capacity
The mean value of the drip loss of the total meat samples was shown as 4.58 with a low standard deviation (0.95). (Table 2). On the other hand, the filter paper press result was shown with the mean value of 49.4 with a relatively wider standard deviation (5.85) (Table 2).
pH at 3 and 24 h post-slaughter
The mean pH value of the total sampled meat measured at 3 h post-slaughter was 6.2 with low standard deviation (0.26), and reduced to the mean value of 5.9 and standard deviation of 0.11 pH level measured at 24 h post-slaughter (Table3).
Effects of age on pH, drip loss, and filter paper press measurements
The age had statistically significant association with the pH measured at 24 h post-slaughter, drip loss and filter paper press (p<0.05) (Table 4).
Association between pre-slaughter rest and pH at 3 h post-slaughter
There was statistically significant association between the pre-slaughter rest and the pH of the meats measured at 3 h post-slaughter (p<0.05) (Table 5).
The pH at 3 h post-slaughter recorded was 6.1 to 6.6 (Table 3). This is comparable with the work of Troy (1999) who recorded 6.1 to 6.37. The higher pH might be due to pre-slaughter stress. Gunenc (2007) stated that pre-slaughter stress has effect on PM pH 3. The pre-slaughter rest of the animals had strong statistically significant (p<0.05) (Table 5), association with PM pH 3 of the meat which agrees with the statement of Lyczynski et al. (2006) that “pre-slaughter stress of animals had statistically significant effect on the early PM pH of meat (p<0.05). This is possibly due to the accumulation of lactic acid in muscle of slaughtered animals which was formed as a result of glycolysis process formed by pre-slaughtering stress of slaughtered animals and it is agreed with the reports of Zhang et al. (2010).
Water holding capacity and drip loss of the meat had statistically significant association with the age of the animals (p<0.05). This statement is supported by the findings of Kashif et al. (2014) who stated that water holding capacity and drip loss varied (p<0.05)(Table 4). between three groups of 1.5 and 2.5 years, and greater than 2.5 years olds animals. These findings also revealed that water holding capacity of meat was found lower in old age of the slaughtered animals. This might be because of higher accumulation of fat and lower moisture content in old age animals comparing to young age animals which is in agreement with the suggestions of Zhang et al. (2010).
CONCLUSION AND RECOMMENDATIONS
Determination of the water holding capacity (WHC) of meat is most important that it is one of the quality indicators of meat. The WHC of the meat was found as 49.4% by filter paper press results and water drip loss was 4.58%. These results were found as having statistically significant associations with age and pre-slaughter rest of the animals. Old age and lack of pre-slaughter rest of the animals resulted in increased ultimate pH level. The prolonged storage of that meat for more than 24 h lead to the spoilage of that meat due to high amount of water in the meat which is conducive for bacterial growth and that could be source of food born diseases and/or cause for the vigorous loss of the profit of the sellers.
The following possible recommendations were forwarded:
(1) Owners of butcher shops should get training on pre-slaughter handling of animals.
(2) Stressed animals should not be approved for slaughter.
(3) The study should be expanded to other breeds and species of animals.
The authors are kindly indebted to thankful the College of Veterinary Medicine, Mekelle University that provided the laboratory and other materials to conduct the research work. They are additionally grateful for “Mekelle Zone Municipality abattoir service rendering unit” that cooperated to conduct the study.
The authors have not declared any conflict of interests.
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